The present invention is related to the field of optical signal distribution and, more particularly, to optical signal distribution through an optical waveguide on an electronic substrate where the optical waveguide is not integral with the electronic substrate.
Optical signal distribution in computers has in recent years been pursued as an attractive alternative and supplement to traditional signal distribution through electrical circuits. As the quest for faster and smaller computers has intensified, the limits of electronic signal distribution have become apparent. Speed is limited by the material of conductors and connectors because of the signal distortion they cause. Higher circuit and wiring densities as well as operating voltage levels magnify and increase problems related to electromagnetic interference (EMI). Optical signals, however, can often travel faster than electrical signals, have a larger bandwidth and are almost insensitive to EMI. An additional advantage of optical signals is that they are less vulnerable to security violations.
Optical signal distribution is generally achieved using optical fiber, optical waveguides or a combination of the two. Both optical fiber and optical waveguides perform the same basic function of guiding light, but the requirements of the specific applications in which they are used are different. Optical fiber, which can be glass or plastic, is typically intended to carry light signals over relatively long distances in environments that may subject it to significant physical stresses. It is cylindrically shaped to minimize attenuation (sharp edges tend to lose light) and coated with buffer layers to maximize robustness. Waveguides, in contrast, are normally intended to carry light signals over relatively short distances in less hostile environments. Because attenuation is less important in short distance connections, and buffer layers are less important in a protected environment, waveguides can be very thin and flat. Because of their reduced bulk, waveguides take up less space than fiber, can be made to bend around corners, and make multiple connections more easily than fiber. These characteristics favor waveguides over fiber for some applications on electronic substrates.
Polymer waveguides in particular are currently being pursued as a low-cost, reliable technique for optical signal distribution between integrated circuit chips on an electronic substrate. Polymer waveguides are typically formed monolithically in single layers using various doping and etching methods in combination with photolithography techniques. These methods are disclosed in more detail in B. Booth, "Low Loss Channel Waveguides in Polymers", The Journal of Lightwave Technology, Vol. 7, pp. 1445-1453, 1989. Waveguides formed in this manner are generally not self-standing and require dedicated space on the surface of the electronic circuit substrate.
Also disclosed in the article referenced in the preceding paragraph is a self-standing multilayered waveguide structure wherein the waveguide is formed as an integral part of the layers by polymerization driven diffusion. The layers are formed from monomers which polymerize when exposed to light. A mask is used to control which portions of the layers are exposed. Monomer diffusions triggered during polymerization create regions of higher refractive index which behave as a waveguide.
Disclosed in IBM Research Disclosure No. 303, "Flexible Interposing Carrier Scheme for Optical Waveguides" (July 1989), is a flexible waveguide structure for connecting optical sources and sinks (devices). The structure can be overlaid on the devices and then optical connections can be made between the flexible waveguide structure and devices.
It is an object of this invention to provide an optical signal distribution system which routes optical waveguides between integrated circuit chips without requiring dedicated space on a circuit substrate.
It is another object of this invention to provide an optical signal distribution system which routes multiple layers of optical waveguides between integrated circuit chips without requiring dedicated space on a circuit substrate.
It is yet another object of this invention to provide an optical signal distribution system in which the waveguide is provided as a preform to the surface of the electronic substrate.
It is still another object of this invention to provide an optical signal distribution system which is removable, thereby rendering the electronic substrate re-workable.
It is still another object of this invention to provide a signal distribution system that is substantially insensitive to electromagnetic interference.